Myocardial leads having rigid helical coils that are turned into heart tissue are disclosed by L. R. Bolduc in U.S. Pat. No. 3,737,579. The helical coils are connected with an elongated flexible conductor to a pacemaker for transmitting electrical pacing currents to the heart. A bipolar electrode having a helical electrode and an annular plate electrode to establish an electrical field through the heart tissue to ensure efficient stimulation of the tissue and minimum current drainage of the power supply of the pacemaker is disclosed by Rockland et al in U.S. Pat. No. 4,010,758. Other types of bipolar electrodes are disclosed by Fischell in U.S. Pat. No. 4,125,116 and Alferness in U.S. Pat. No. 4,355,642. These patents show tissue stimulation electrodes structure having central electrode surrounded by secondary electrodes for applying pacing and defibrillation pulses to the heart.